Anisotropic Excitons Reveal Local Spin Chain Directions in a van der Waals Antiferromagnet

Congratulations to Chunhao Guo, Kejun Li and Prof. Yuan Ping for their work in collaboration with Dong Seob Kim, Di Huang, Dario Rocca, Frank Y. Gao, Jeongheon Choe, David Lujan, Edoardo Baldini, Li Yang, Shivani Sharma, Raju Kalivanan, Raman Shankar, Shang-Fan Lee and Xiaoqin Li on “Anisotropic Excitons Reveal Local Spin Chain Directions in a van der Waals Antiferromagnet”, published in Advanced Materials!  Link to the published article. 

Abstract: A long-standing pursuit in materials science is to identify suitable magnetic semiconductors for integrated information storage, processing, and transfer. Van der Waals magnets have brought forth new material candidates for this purpose. Recently, sharp exciton resonances in antiferromagnet NiPS3 have been reported to correlate with magnetic order, i.e., the exciton photoluminescence intensity diminishes above the Néel temperature. Here, we find that the polarization of maximal exciton emission rotates locally, revealing three possible spin chain directions. This discovery establishes a new understanding of the AFM order hidden in previous neutron scattering and optical experiments. Furthermore, we suggest defect-bound states as an alternative exciton formation mechanism that has yet to be explored in NiPS3. Our supporting evidence includes chemical analysis, excitation power and thickness dependent photoluminescence, and first-principles calculations. This mechanism for exciton formation is also consistent with the presence of strong phonon side bands. Our study shows that anisotropic exciton photoluminescence can be used to read out local spin chain directions in antiferromagnets and realize multi-functional devices via spin-photon transduction.

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